Magnetic disk system

ABSTRACT

A magnetic disk system comprises a magnetic head for writing data on and reading data from a magnetic disk as a recording medium and a magnetic disk unit having a head positioning mechanism for positioning the magnetic head on a selected track of the magnetic disk without forming servo information on the magnetic disk. The magnetic head comprises an MR film which is disposed parallel to the direction of the width of a track of the magnetic disk, current supplying electrodes disposed to be in contact with both ends of the magnetic film which are opposed in the direction of the track width and a signal detecting electrode disposed between the current supplying electrodes to be in contact with the MR film. The width of the signal detecting electrode is less than 1/3 of that of the current supplying electrodes. The magnetic disk system permits highly accurate alignment of the magnetic head with closely spaced tracks.

CROSS-REFERENCES TO THE RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/766,326 filed on Sep. 27, 1991, now U.S. Pat. No. 5,331,492.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic disk system constructed froma magnetic head assembly and a magnetic disk unit, and more particularlyto a magnetic disk system having a magnetic disk unit which has afeature which permits at least one magnetic head to be positioned on aselected data track accurately without the necessity of forming servoinformation on the disk and a magnetic head assembly which is suitablefor its alignment with a track (i.e. tracking) and its azimuthalignment.

2. Description of the Related Art

In general, with a magnetic disk unit, it is required to accuratelyposition a magnetic head on data tracks of a magnetic disk at the timeof reading of information from or writing of information on the disk.Heretofore, tracking servo systems for positioning a head on tracksinclude the following systems.

(1) The servo-surface servo system which uses a dedicated servo surface.

(2) The data-surface servo system which uses servo information recordedon a data surface.

(3) The servo-surface and data-surface combined system which uses both aservo surface and a data surface in combination.

In the first place, with the servo-surface servo system, servoinformation is formed over the whole of a certain surface (e.g. servosurface) of more than one disk surface and the servo information iscontinuously read to permit a servo head on the servo surface to trackservo tracks correctly. A data head, which is mounted on the samecarriage as the servo head and makes access to another disk surface(e.g. data surface), interlocks the head on the servo surface to makeaccess to a data track corresponding to a servo track. With theservo-surface servo system, when expansion and contraction of the disksoccur due to variations in temperature and humidity, a problem arises inthat the head will go off a data track (i.e. thermal off-truck)depending on a difference in expansion and contraction between disksurfaces. In addition, the servo-surface servo system uses the whole ofa surface of a disk as the servo surface and thus formatting efficiencywill be decreased particularly when the number of disks is small.

With the sector servo system which is a type of the data surface servosystem, servo information is formed on a part of sectors, i.e., a servosector. The so-called sampled value control system for tracking is usedwhich permits the servo information to be read by the head which makesaccess to a data surface for reading or writing. With the sector servosystem, since the servo information is demodulated for each of the datasurfaces to position a corresponding head on a selected track, suchthermal off-track as described above will never occur. According to themethod, the tracking servo is performed by the sample value controlbecause the servo information is read intermittently for each of servosectors. Compared with the above-described servo-surface servo system inwhich servo signals are continuously obtained, therefore, a wide servoband cannot be achieved. The trackability will be poor if it is assumedthat there is no thermal off-track. In the sector servo system, thesettling-time is longer and the disturbance-proof performance is alsopoorer.

with the servo surface and data surface combined system, on the otherhand, the servo information is formed on each data surface with theservo head positioned on a servo track on the servo surface, whereas inthe servo-surface servo system, data is read from or written on a datasurface by the data head with the servo head positioned on a track onthe servo surface. The servo information is formed on a part of servosectors, i.e., the servo sector. From the servo information formed inthe servo sector on the data surface is obtained a position signal(information indicating the position of the head relative to a track)which is in a low frequency range and contains a DC (Direct Current)component which is used to perform tracking control. In the combinedsystem as well, the format efficiency is poor and the circuitry used iscomplex in construction. Because there is the necessity of servoformatting as well as data formatting, a problem will arise in that ittakes a long time to establish and implement the system.

The demand for higher recording density in magneticrecording/reproducing apparatus such as magnetic disk units has beenincreasing recently. For a higher recording density, the track densityand linear density must be increased. Narrowing the width of tracks willalso be required. As a magnetic recording medium used has been made ofnot only a longitudinal recording medium on which information isrecorded using the usual recording method but also a perpendicularrecording medium and an obliquely evaporated/sputtered recording medium.Under such conditions, it has been required that the registration of aread/write head with tracks on a magnetic recording medium and theazimuth alignment be performed more precisely. In order to detect trackoffset and azimuth offset necessary for the registration and azimuthalignment of a head, a specific type of magnetic head has been used.

FIG. 36 illustrates an example of a conventional magnetic head whichuses two induction type heads to detect track offset. That is, magneticcores 101 and 102 consisting of a soft magnetic material are disposedside by side in the direction of the width (indicated by W) of a trackand coils 103 and 104 are wound around the magnetic cores 101 and 102,respectively. Supposing outputs of the induction type heads to be V1 andV2, respectively, when the head positions right over the track, thefollowing equation will hold.

    V1-V2=0

When the head does not position right over the track, the followingrelationship will hold.

    V1-V2=0

Thus, the track offset is detected from the difference magnitude betweenV1 and V2 and the azimuth can be detected from the difference in phasebetween V1 and V2.

With the arrangement of FIG. 36 in which two inductive-type heads eachhaving a magnetic core wound with a coil are disposed side by side,however, a space must be secured to permit the coils to be wound aroundthe cores and the dimension of the heads in the direction of width of atrack must be made large. Thus, the conventional head shown in FIG. 36will have a structure which is not suited to narrow the tracks of adisk.

As a magnetic head which needs no coil, on the other hand, there is anMR head which uses Magnetoesistance (MR) film having themagnetoresistance effect. FIG. 37 illustrates which is referred to as ayoke type MR head which uses a yoke (i.e., magnetic core) to conductleakage flux from a magnetic recording medium to an MR film. The MR headis constructed from a lower core 201, separated upper cores 203 and 204disposed above the lower core with a read/write gap 202 disposedtherebetween, an MR film 205 disposed between the upper cores 203 and204 and electrodes 206 and 207 connected to the both ends of the MR film205.

FIGS. 38A and 38B illustrate conventional shield type MR heads having ashielding function by an MR film. As shown in FIG. 38A, between thatends of magnetic cores 208 and 209 which form a recording/reproducinggap are disposed tips of an MR film 205 and electrodes 208 and 209. InFIG. 38B, between a magnetic core 208 disposed below a magnetic core 209and a newly provided shielding plate 200 are disposed an MR film 205 andelectrodes 206 and 207. In the case of FIG. 38B, a recording gap isformed between ends of the magnetic cores 208 and 209, while areproducing gap is formed between the magnetic core 208 and the shieldplate 200.

Of the conventional tracking servo systems for placing a head on tracks,the servo-surface servo system using a dedicated servo surface has theoff-track problem (a) in which the head cannot be placed on a selectedtrack correctly depending on a difference in expansion and contractionbetween disk surfaces which is due to variations in temperature andhumidity, and the poor formatting efficiency problem (b) arising fromthe fact that the whole of a surface of a disk is used as a servosurface only.

Of the data-surface servo systems, the sector servo system in particularhas not the off-track problem but problems (c) in that not only thetrackability is poor because the servo band cannot be made high by theuse of the sampled value control system but also the settling-time islonger and the disturbance-proof performance is poorer.

The servo-surface and data-surface combined system is poor in formatefficiency and complex in circuit arrangement. Moreover, the problem (d)arises in that it takes a long time to establish and implement thesystem because servo formatting must be performed on a data surface inaddition to data formatting.

In the conventional magnetic head assembly, as described above, twoinductive-type heads are disposed adjacent to each other in thedirection of the width of a track in order to detect track offset andazimuth offset. With the magnetic head assembly of such a structure,however, the problem (e) arises in that its structure becomes unsuitablefor narrowing tracks because its dimension along the width of a trackhas to be made large because of the necessity of securing a space forwinding coils.

SUMMARY OF THE INVENTION

The present invention is directed to the provision of a magnetic disksystem which has a magnetic head and a magnetic disk unit which permitvarious problems (a) to (e) associated with the conventional trackingservo systems to be solved.

It is therefore a first object of the present invention to provide amagnetic disk system having a magnetic disk unit which permits thecorrect placement of a head on data tracks by obtaining a positionsignal indicating the position of the head relative to data tracks fromdata tracks of each disk surface without the necessity of recording anytracking servo information.

It is a second object of the present invention to provide a magneticdisk system having a magnetic head assembly which permitshigh-sensitivity detection of track offset and azimuth offset even whenthe conventional problems are solved and narrowing of disk tracks isrealized.

As a magnetic head for use in a magnetic disk system of the presentinvention, a composite head assembly is used which comprises at leastone recording head for recording data on data tracks of a magnetic diskand at least two reproducing heads disposed parallel to the direction ofa radial line of the magnetic disk for obtaining reproduced outputsindependently, the recording head and the reproducing heads being formedintegral with each other. The difference between the reproduced outputsof the reproducing heads or the difference between the reproducedoutputs which have been subjected to peak detection or synchronousdetection is obtained to produce a position signal indicating therelative position of the magnetic head assembly with respect to a datatrack. By the use of the position signal the magnetic head assembly iscontrolled so that it is positioned on a selected track.

In the present invention, a prescribed formatting signal is recorded ondata tracks by the recording head while displacement of the magnetichead assembly is detected from the outside of the magnetic disk. Whendata is recorded on data tracks, the position signal is used to positionthe magnetic head on a selected track in an area other than a datarecording area on the track. In the data recording area, on the otherhand, a position signal, which has been obtained immediately before theinitiation of data recording and held since then, is used to positionthe magnetic head on a selected data track.

When a formatting signal is recorded on an unrecorded magnetic disk,displacement of the magnetic head assembly along a radial line of thedisk is detected from the outside of the disk. The head positioningcontrol is performed at a predetermined track pitch on the basis of theamount of displacement of the head assembly so as to record theformatting signal over the whole surface of the disk. When data isreproduced from a recorded track, the tracking control of the head isperformed using a position signal produced as described above.

In the seek control from a track to another track, the current positionof the head can be detected by detecting the number of tracks that thehead crossed on the basis of the position signal obtained from thereproduced outputs of the reproducing heads, which may be subjected tosignal processing. At the same time, feedback speed control is performedon a desired speed curve which is a control index up to a selected trackusing speed information obtained by detecting the displacement of themagnetic head from the outside of the disk.

A magnetic head according to a first aspect comprises a magnetic film(e.g., an MR film) disposed substantially parallel to the direction ofthe width of a track of a magnetic recording medium and having themagnetoresistance effect, at least one pair of current supply electrodesdisposed to be in contact with both ends or their neighborhoods of themagnetic film in the direction of the width of a track and at least onesignal detect electrode disposed between the current supply electrodesto be in contact with the magnetic film, the signal detect electrodebeing smaller in width than the current supply electrodes. It isdesirable that the width of the signal detect electrode be below 1/3 ofthat of the current supply electrodes.

The magnetic head may further comprises a magnetic core (e.g., a yoke)for conducting leakage flux from the magnetic recording medium to themagnetic film. It is desirable that that part of the magnetic core whichis nearer to the magnetic recording medium be magnetically divided intosections (e.g., two sections).

A magnetic head according to a second aspect comprises first and secondmagnetic detecting elements (including MR films). Each of the first andsecond magnetic detecting elements comprises a magnetic film disposedsubstantially parallel to the direction of the length of a track of amagnetic recording medium and having the magnetoresistance effect and atleast one pair of electrodes disposed to be in contact with both ends ortheir neighborhoods of the magnetic film which are opposed in thedirection of the length of the track. Between the first and secondmagnetic detecting elements is disposed a magnetic core for conductingleakage flux from the recording medium to the magnetic films of thefirst and second magnetic detecting elements. It is desirable that thatpart of the magnetic core which is nearer to the magnetic recordingmedium be magnetically divided in the direction of the track width.

In the magnetic disk unit of the present invention, the position signalrequired to position the head on a selected track is obtained fromreproduced outputs of the reproducing heads as described above. Thus,the following advantages will be obtained.

(1) There is no need of recording head positioning servo information ona magnetic disk. The formatting efficiency improves.

(2) The thermal off-track problem due to expansion and contraction of adisk will be resolved because the position signal is continuouslyobtained from signals on data tracks.

(3) The servo band becomes wide, so that the trackability, settlingcharacteristics and disturbance resisting characteristics improve. Thispermits accurate positioning of the head on a data track.

(4) There is no need for both the data formatting and servo formatting.Thus, the time it takes to establish and implement the system isshortened.

The magnetic head according to the first aspect has the followingadvantages.

(5) By disposing the magnetic film (e.g., the MR film) having themagnetoresistance effect in the direction of the track width, producinga constant current flow in the MR film through the current supplyelectrodes and detecting a voltage difference corresponding to theamount of track offset or azimuth offset through the signal detectelectrodes, the necessity of adjoining two heads in the direction of atrack can be eliminated and the size of the head in the direction of thetrack width can be made small.

(6) By making the signal detect electrode smaller in width than thecurrent supply electrodes, the area of a portion which is adapted todetect leakage flux from the magnetic recording medium can be madelarge. Thus, even if the data tracks are made narrower, the track offsetand azimuth offset can be detected with a high sensitivity.

(7) By magnetically dividing that portion of the magnetic core which isnearer to the magnetic recording medium in the direction of the trackwidth, leakage flux from each of the right and left portions of a trackis conducted to a corresponding respective MR film. Thus, the trackoffset and azimuth offset can be detected with a higher sensitivity.

Moreover, with the magnetic head according to the second aspect, firstand second magnetic detecting elements, each of which comprises an MRfilm disposed substantially parallel to the direction of the length of atrack and at least one pair of electrodes disposed to be in contact withthe MR film, are disposed apart from each other in the direction of thetrack width. The first and second magnetic detecting elements detects avoltage difference or a current difference corresponding to the amountof track offset or azimuth offset. Thus, the head has the followingadvantages.

(8) The necessity of winding a coil around each magnetic detectingelement as in an induction head is eliminated. The size of the entirehead in the direction of the track width can be made small.

(9) The MR film is disposed substantially parallel to the direction ofthe length of a track and there is no limit to the size in thisdirection. Thus, the area of a portion which is adapted to detectleakage flux emerging from the magnetic recording medium can be madelarge. In the case of a disk with closely spaced tracks, therefore, thetrack offset and azimuth offset can be detected with a high sensitivity.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1A is a perspective view of a first embodiment of a magnetic headassembly which is used in a magnetic disk system of the presentinvention;

FIG. 1B is a perspective view of a modification of the first embodimentof the present invention;

FIG. 2A is a plan view of the essential part of the magnetic headassembly of FIG. 1:

FIG. 2B is a plan view of the essential part of a magnetic head assemblywhich is a modification of the magnetic head of FIG. 1;

FIG. 2C is a plane view of the essential part of a conventional magnetichead;

FIG. 2D is a sensitivity distribution diagram of the conventionalmagnetic head in FIG. 2C;

FIG. 2E is a plan view of the essential part of a magnetic head;

FIG. 2F is a sensitivity distribution diagram of the magnetic head inFIG. 2E;

FIG. 2G is a perspective view of the magnetic head on a magnetic disk;

FIG. 3 is a plan view of the essential part of a second embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 4 is a cross-sectional view taken along line C-C' of FIG. 4;

FIG. 5 is a plan view of the essential part of a third embodiment of themagnetic head assembly which is used in the magnetic disk system of thepresent invention;

FIG. 6 is a plan view of the essential part of a fourth embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 7 is a plan view of the essential part of a fifth embodiment of themagnetic head assembly which is used in the magnetic disk system of thepresent invention;

FIG. 8 is a plan view of the essential part of a sixth embodiment of themagnetic head assembly which is used in the magnetic disk system of thepresent invention;

FIG. 9 is a plan view of the essential part of a seventh embodiment ofthe magnetic assembly head which is used in the magnetic disk system ofthe present invention;

FIG. 10 is a plan view of the essential part of a seventh embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 11 is a plan view of the essential part of a ninth embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 12 is a plan view of the essential part of a tenth embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 13 is a plan view of the essential part of an eleventh embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 14 is a plan view of the essential part of a twelfth embodiment ofthe magnetic head assembly which is used in the magnetic disk system ofthe present invention;

FIG. 15 is a plan view of the essential part of a thirteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 16 is a plan view of the essential part of a fourteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 17 is a plan view of the essential part of a fifteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 18 is a plan view of the essential part of a sixteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 19 is a plan view of the essential part of a seventeenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 20 is a plan view of the essential part of a eighteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 21 is a plan view of the essential part of a nineteenth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention;

FIG. 22 is a plan view of the essential part of a twentieth embodimentof the magnetic head assembly which is used in the magnetic disk systemof the present invention:

FIG. 23 is a plan view of the essential part of a 21st embodiment of themagnetic head assembly which is used in the magnetic disk system of thepresent invention;

FIG. 24 is a plan view of the essential part of a twenty-secondembodiment of the magnetic head assembly which is used in the magneticdisk system of the present invention;

FIG. 25 illustrates a relationship between track offset and envelopedifference of the magnetic head according to the present invention:

FIGS. 26A, 26B and 26C are a front view, a plan view and a side view,respectively, of still another embodiment of the magnetic head assemblyused in the magnetic disk unit of the present invention;

FIGS. 27A and 27B are a front view and a plan view of the magnetic headassembly of FIG. 26 for explaining the essential part of the reproducinghead in detail;

FIG. 28 is a circuit diagram of a reproducing circuit used with thereproducing head;

FIG. 29 is a functional block diagram of a magnetic disk unitconstituting the magnetic disk system of the present invention;

FIG. 30 is a functional block diagram of a head positioning controlsystem for initial formatting of a disk;

FIG. 31 is a waveform diagram of two-phase position signals detectedfrom an optical sensor unit constituting the magnetic disk unit of FIG.29;

FIG. 32 illustrates a relationship among the position of the magnetichead, peak values of the reproduced output of the reproducing head andposition signals for head positioning;

FIG. 33 illustrates a relationship among the position of the magnetichead, the synchronous detect output of the reproduced output from thereproducing head and the position signals;

FIG. 34 illustrates a relationship between position signals in themagnetic disk unit and track pulses generated by a track pulsegenerator;

FIG. 35 illustrates a two-phase position signal obtained from an opticalsensor unit constituting the magnetic disk unit and a position signalconverted by a position signal producing circuit;

FIG. 36 is a perspective view of a conventional induction type magnetichead;

FIG. 37 is a perspective view of a conventional yoke type MR head;

FIG. 38A is a perspective view of a conventional shield type MR head;and

FIG. 38B is a perspective view of another conventional yoke type MRhead.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A magnetic disk system of the present invention is constructed from amagnetic head assembly which writes data on or reads data from amagnetic disk serving as a recording medium and a magnetic disk unitwhich reproduces an electric signal from a magnetic signal recorded on atrack while causing the magnetic head assembly to track the trackcorrectly.

In the first place, a description will be made of a magnetic headassembly used in the magnetic disk system of the present invention withreference to FIGS. 1A, 1B, 2A and 2B.

FIGS. 1A and 1B are perspective views of a first embodiment and it'smodification of the magnetic head assembly constituting the magneticdisk system of the present invention, and FIGS. 2A and 2B are each aplan view of that essential part of the head assembly which is near toan MR film 15. The magnetic head (hereinafter referred to as the head)is featured by a structure in which the magnetic material film (MR film)15 having the magnetoresistance effect is disposed in the direction ofthe width of a track of the magnetic recording medium.

The magnetic head assembly 1 is constructed from a lower core 11consisting of a soft magnetic material, an MR film 15 which is disposedsubstantially parallel to the direction of the track width of a magneticrecording medium (not shown) in such a way that it is sandwiched betweenthe lower core 11 and upper core 13, (14) with a gap 12 formed betweenit and the lower core, a pair of current supply electrodes 16 and 17disposed at both ends of the MR film 15 which are opposed in thedirection of the track width and a signal detect electrode 18 which isdisposed to contact the MR film 15 at the middle point between thecurrent supply electrodes 16 and 17. The head assembly is characterizedin that the width of the signal detect electrode 18 is smaller that ofeach of the current supply electrodes 16 and 17.

In the magnetic head 1 constructed as described above, when the tips ofthe upper core 13, (14) and the lower core 11, which are magnetic cores,are disposed to face the magnetic recording medium, leakage fluxresulting from signals recorded on tracks of the magnetic recordingmedium flows into the MR film 15 via the cores 11 and 13, (14). Theelectrical resistance of the MR film varies according to the amount ofleakage flux flowing thereinto. At this point, a flow of a constantdirect current is produced in the MR film 15 by the current supplyelectrodes 16 and 17, thereby producing a voltage V1 between theelectrodes 16 and 18 and a voltage V2 between the electrodes 17 and 18.A difference in magnitude between the voltages V1 and V2 permits trackoffset to be detected and a difference in phase between V and V2 permitsazimuth offset to be detected. The use of these detect signals permitthe alignment with tracks and azimuth alignment of the read/write head.

In the above case, that part of the MR film 15 which contacts the signaldetect electrode 18 forms insensitive region (so called dead zone) inwhich variations in electrical resistance do not contribute to thevoltages V1 and V2. In order to explain the above phenomenon, arelationship between the track off-set of the head assembly and thedifference in magnitude between V1 and V2 is depicted graphically inFIG. 25. In the figure, the track width and the dead-zone width areindicated by TW and β, respectively. In order for the head to track atrack correctly, the servo control is performed so that the differencein magnitude, that is, the position signal will become zero.

In the servo control, the higher the S/N ratio of the position signal,the more the accuracy with which the head is positioned on a selectedtrack increases. The wider the linear range of the position signal withrespect to the track center, the higher the stiffness againstdisturbance and the less the positioning error. However, as the width ofthe dead zone increases, the S/N ratio of the position signal decreasesand the linear region of the position signal narrows as may be seen fromFIG. 25.

That is, for the linear range obtained when β=0 (k=∞) in equationβ=TW/k, a mere narrow linear expressed by 1-1/k is obtained.

According to the rule of thumb, in order to perform good servo controlit is desired that the linear range be 2/3 or more of the track widthTw. In other words, the width β of the dead zone, i.e., the width of thesignal detect electrode 18 must be set to 1/3 or less of the track widthTW. Also, in order to permit high-sensitivity detection of azimuthoffset under the high ratio condition, it is desired that the signaldetect electrode 18 be narrow in width.

By coupling a recording thin film coil (not shown) with the lower core11 or the upper cores 13, (14), the use of the magnetic head assemblyaccording to the present embodiment as a read/write head is allowed. Asa reproduced signal in this case, use may be made of, for example, a sumsignal of V1 and V2.

As explained in the first embodiment, in the servo system using threeterminal heads, a peak value PA of a signal SA read from a currentsupply electrode 16 and a signal detect electrode 18 (so called centralelectrode) and a peak value PB of a signal SB read from a signal detectelectrode 18 and a current supply electrode 17 are equal to each other.In this case, the peak value PA is an envelope value, which can beobtained after half-wave rectifying or full-wave rectifying the signalSA, and the peak value PB is an envelope value, which can be obtainedafter half-wave rectifying or full-wave rectifying the signal SB. Inother words, a tracking is performed so as to establish the followingequation.

    P=PA-PB=0

In this case, as a prerequisite condition, it is essential that theamplitude of the signal SA and that of the signal SB be completely thesame. If these signals SA and SB are different from each other in theamplitude, an off-track, which is proportional to its error, isgenerated.

However, in general, the MR head has a characteristic of an asymmetricaldistribution curve (∩) in a reproducing sensitivity distribution in adirection of a track width of the MR film based on the following reason(cf. FIG. 2D).

In a case that the central electrode 18 is provided at the centralposition between the electrodes 16 and 17, there is generated adifference between the signals SA and SB in the amplitude when the headis in an on-track state since the producing sensitivity distribution isasymmetrical to the axis passing the central position. As a result,there is a case that an error will occur in the tracking operation.

In the MR head using a principle in which a signal is detected based onthe the variation of the resistance of the MR film in accordance withthe change of the magnetic direction (e.g., magneto-resistive effect),the following current supply is performed in order to increase thevariation rate of the resistance and effectively detect the signal.

More specifically, a bias current is supplied between the electrodes 16and 17 such that the magnetic direction of the MR film has aninclination of about several tens degrees (at least <90°) to a verticaldirection from the surface of the recording medium.

However, in actual, the magnetization is not uniformly rotated in the MRfilm between the electrodes 16 and 17. Due to such a magnetic rotation,as shown in FIG. 2D, the reproducing sensitivity distribution curve (∩),which presents the maximum peak of the reproducing sensitivity detectedat a point (position Xc) being slightly out of the physical centralposition 0 (as origin) between both electrodes, and which isasymmetrical to the vertical axis passing the origin, is resultinglydrawn. The graph of FIG. 2D is the curve graph showing one example ofactual data of the reproducing sensitivity distribution of a suitablebias current value in a direction of a track width. In other words, Thegraph of FIG. 2D shows the reproducing sensitivity distribution of themagnetic head 1 having the different structure from the magnetic head ofFIG. 2E. More specifically, the magnetic head 1 of FIG. 2D comprises twoelectrodes 16 and 17. Unlike the magnetic head of FIG. 2E, the centralelectrode 18 is not provided in the vicinity of the central portionbetween electrodes 16 and 17. However, in the case of the magnetic headof FIG. 2E comprising three electrodes 16, 17 and 18, since the centralelectrode 18 is used to detect a signal in which no supply of the biascurrent is performed, no influence is exerted upon the reproducingsensitivity distribution itself. Therefore, even in the above twodifferent types of terminal structure, the asymmetry of the graph curveis similarly formed. As the other factor, which brings about theasymmetry of the graph curve, there can be considered ununiformity ofthickness of the MR film 15, which may be generated in the manufacture.

In consideration of the above point, the following embodiment willexplain further improvement.

More specifically, the central electrode 18 of this embodiment isattached to a predetermined position on the MR film 15 such that theamplitude of the signal SA read from the electrode 16 and the centralelectrode 18 in the on-track state and that of the signal SB read fromthe central electrode 18 and the electrode 17 are equal to each other.The position of the attachment of the central electrode 18 is specifiedby the following method.

(1) First of all, in a case of a suitable bias current value having thesmallest wave distortion, the reproducing sensitivity distribution ofthe MR film 15 is measured.

(2) Based on the measured reproducing sensitivity distribution, afunction of the reproducing sensitivity distribution is defined asRs(x), and obtain a relative position xc from the physical centralposition (i.e., origin x=0) such that the following equation of anintegral can be established.

Integral value of Rs(x) from minus infinity to xc=integral value ofRS(x) from xc to plus infinity, that is: ##EQU1## wherein x: position ofthe track width direction (value of coordinate x).

(3) The central electrode 18 is attached to the relative position xcfrom the central position (i.e., x=0) between both electrodes 16 and 17.

The above-mentioned method, that is, in the case that the center betweenthe electrodes 16 and 17 provided to be spaced from each other isdefined as the origin x=0, the position, which is from the origin to therelative position xc, where the central electrode 18 is provided, iscalculated as a suitable position where the central electrode isactually provided, in order to obtain the position of the centralelectrode 18 extending to the distance xc from the origin.

By the above calculation method of the suitable position of the centralelectrode 18, the above-mentioned disadvantage is improved by realizingthe MR head based on the above method for specifying the actual positionon the sensitivity when the magnetic head is actually used in order notto generate the offset on the sensitivity as the theoretically productbased on only the size of the design of the other example.

However, even in the MR head 1 having the structure in which threeterminals are suitably provided, there may actually occur a case that anerror in attaching the central electrode 18 to the correct position willbe generated during the assembly.

As a result, a slight error will be generated in amplitude of each ofthe signals SA and SB. Also, in a case that the bias current when the MRhead 1 is designed and the bias current when the MR head 1 is actuallyused are different from each other, the change of the characteristic ofthe MR film 15, which is caused by the temperature change when the MRhead is actually used, can be also be considered as a factor ingenerating the above-mentioned error.

Therefore, it is desirable that the error be corrected during theoperation by the following method of other embodiment.

More specifically, a ratio R of amplitude MA to amplitude MB(reproducing signal width=MA/MB) in the signals SA and SB in theon-track state is obtained in advance. Then, a position signal P', whichis obtained correcting a position signal P by use of the ratio R, iscalculated based on the following equation, and the calculated value isused in correction control at the time of operation, therebysequentially correcting the movement of the head without generating theoff-track at the time of operation.

    P'=(PA-PB)·R=(PA-PB)·MA/MB

wherein PA=an envelope value, which can be obtained after half-waverectifying or full-wave rectifying the signal SA, and PB=an envelopevalue, which can be obtained after half-wave rectifying or full-waverectifying the signal SB.

The above point can be shown by a broken line of FIG. 25 showing therelationship between an envelope difference and a track offset.

For obtaining the above reproducing signal width ratio R, which is thesame as in the on-track state, as shown in FIG. 2G, in a region wheredata of the disk 21 opposite to the MR head 1 is neither recorded norreproduced, a signal of the fixed cycle is recorded to have a widertrack width Tw than the reproducing width Rw of the MR head 1 over onecircumference. In this case, even in a state that tracking servo controlis not performed, it is essential that the track width Tw be ensured tobe sufficiently wide in order that the reproducing section having thewidth Rw (region between terminals 16 and 18) does not deviate from thetrack width Tw. Therefore, the above-mentioned conditions are satisfied,the reproducing signal width ratio R, which is the same as in theon-track state, can be always obtained.

More specifically, in the MR head 1, the signal having theabove-mentioned fixed frequency is recorded in the innermost peripheryor outermost periphery of the track of the retracting disk. In thiscase, the track width Tw of the signal may be set such that the spacewider than the track vibration Vw is ensured between both sides of thetrack. It is desirable that the track width Tw be sufficiently widelyensured. Therefore, according to the present invention, the relationshipbetween the track width Tw and the width Rw of the reproducing sectionof the head 1 in the size is set so as to satisfy either one of thefollowing two expressions.

Tw>>Rw, Tw>Rw+Vw

By providing the above-mentioned correction method and setting the aboverelationship in the size, the following errors can be real-timely anddynamically corrected.

More specifically, the error of the attachment of central electrode 18,which is caused during the actual assembly, and the factor in the error,which is caused when the MR head is actually used, e.g., the case thatthe MR head 1 is used in the state that the bias current value differs,and the change of the characteristic of the MR film 15, which is causedby the temperature change when the MR head is actually used.

Therefore, the MR head 1, which can perform an ideal characteristic, canbe realized.

According to the present invention, by a plurality of improvements inboth cases that the magnetic head is designed and that the magnetic headis actually used, there can be provided a magnetic disk system having anMR head having not only an ideal static characteristic as an MR head inthis technical field but also an dynamic characteristic, which can solvethe disadvantages by the dynamic correcting process.

FIG. 3 is a plan view of that part of a magnetic head according to asecond embodiment which is near to an MR film. The second embodiment isdistinct from the first embodiment in that the signal detect electrode18 is formed to contact only that part of the MR film which is nearer tothe direction M of the magnetic recording medium. According to thesecond embodiment, variations in electrical resistance in that part ofthe MR film 15 to which the leakage flux from the magnetic recordingmedium is localized is detected efficiently as a detect signal of V1-V2,thus permitting high-sensitivity detection of the track offset andazimuth offset.

FIGS. 4 and 5 are a plan view and a cross-sectional view, respectively,of the essential part of a magnetic head according to a thirdembodiment. In order to permit the signal detect electrode 18 to contactonly that portion of the MR film 15 which is nearer to the runningdirection of the magnetic recording medium as in the second embodiment,an insulation film 19 is formed between the MR film 15 and the electrode18 so that only the tip of the electrode 18 contacts the MR film 15. Itgoes without saying that the second embodiment also offers the sameadvantage as the second embodiment.

The same advantage will be obtained by forming that end of the signaldetect electrode 18 which is nearer to the magnetic recording medium asshown in FIG. 2B. In this case, it is possible to secure a wide area forthe flux sensing portion. The manufacture of a wide electrode is easierthan that of a thin electrode.

FIG. 4 is a plan view of the essential part of a magnetic head assemblyaccording to a fourth embodiment. In this embodiment, there are provideda first signal detect electrode 21 which contacts that portion of the MRfilm 15 which is nearer to the direction M of the magnetic recordingmedium and a second signal detect electrode 22 which contacts that partof the MR film 15 which is disposed at the opposite side to thedirection M of the magnetic recording medium, i.e., which is thefarthest from the magnetic recording medium. In the fourth embodiment,voltages V1, V2, V3 and V4 are detected between the current supplyelectrode 16 and the first signal detect electrode 21, between thecurrent supply electrode 17 and the electrode 21, between the currentsupply electrode 16 and the second signal detect electrode 22 andbetween the electrode 17 and the electrode 22, respectively.

In this embodiment, when the magnetic head is placed off a track in thedirection of the track width, there is a difference in amount of fluxbetween the first and second portions of the MR film 15, the firstportion lying between the current supply electrode 16 and the firstsignal detect electrode 21 which is placed nearer to the direction ofthe magnetic recording medium and the second portion lying between thecurrent supply electrode 17 and the first signal detect electrode 21.However, the amount of flux between the current supply electrode 16 andthe signal detect electrode 22 is substantially equal to that betweenthe current supply electrode 17 and the second signal detect electrode22. The amount of flux in this case is approximately half of the totalamount of flux flowing into the MR film. Thus, by making a comparison inmagnitude between V1 or V2 and V3 or V4, it becomes possible to seewhether or not the magnetic head assembly is placed off a track.

FIG. 7 is a plan view of the essential part of a magnetic head accordingto a fifth embodiment. In this embodiment, between the current supplyelectrodes 16 and 17 are disposed two or more signal detect electrodes23 to 26 (four in this example) symmetrically with respect to the centerline of the MR film. The width of each of the signal detect electrodes23 to 26 is narrower that that of the current supply electrodes 16 and17. When constant direct current flows into the MR film 15 through thecurrent supply electrodes 16 and 17, voltages V5 and V6 are producedbetween the signal detect electrodes 23 and 24 and between the signaldetect electrodes 25 and 26, respectively. The detection of the voltagedifference and phase difference between V5 and V6 permits track offsetand azimuth offset to be detected.

According to the present embodiment, by placing the signal detectelectrodes 23 to 26 in the position to permit the voltages V5 and V6 tobe detected with higher sensitivity, variations in flux flowing from themagnetic recording medium into the MR film 15 can be detected moreaccurately as a voltage signal indicating the difference between V5 andV6.

FIG. 8 is a plan view of the essential part of a magnetic head accordingto a sixth embodiment, in which between current supply electrodes 16 and17 are disposed more signal detect electrodes 31 to 35 symmetricallywith respect to the center line of the MR film. The width of each of thesignal detect electrodes 31 to 35 is narrower than that of the currentsupply electrodes 16 and 17. In this case, a voltage V7 between theelectrodes 16 and 31, a voltage between the electrodes 32 and 33, avoltage V9 between the electrodes 33 and 34 and a voltage V10 betweenthe electrodes 35 and 17 are detected when a constant flow of directcurrent is produced in the MR film 15 through the current supplyelectrodes 16 and 17. Further, the voltage difference and phasedifference between V7 and V10 and between V8 and V9 are obtained todetect the track offset and azimuth offset.

According to the present invention, the inclination of the magnetic headin the direction of the track width can be detected with highsensitivity on the basis of the difference between a symmetrical pair ofvoltage: V7 and V10; and V8 and V9.

FIG. 9 is a plan view of a magnetic core of a magnetic head assemblyaccording to a seventh embodiment. The core nearer to the magneticrecording medium is divided into two pieces indicated at 13a and 13balong the track width, thereby dividing the leakage flux flowing fromthe magnetic recording medium into two. The flux flowing into the MRfilm 15 is also divided into two in the direction of the track width.Thus, the voltage difference and phase difference between voltages, V1,V2, V3, V4, V5, V6, V7, V10, V8, V9 can be detected with highersensitivity.

FIG. 10 is a plan view of a magnetic core of a magnetic head accordingto an eighth embodiment. Between the divided upper cores 13a and 13b isdisposed a superconducting film 37. In the case of the eighthembodiment, the leakage flux from the magnetic recording medium flows toavoid the superconducting film 37. Thus, the flux flows completelyseparated into the upper cores 13a and 13b, offering the same advantageas obtained in the eighth embodiment more remarkably.

FIG. 11 is a plan view of a magnetic core of a magnetic head accordingto a ninth embodiment. A notch 40 is formed at the center of that eachof the upper cores 13 and 14 which is located on the center of the MRfilm 15. With such a shape, that end portion of the core 13 which isnearer to the magnetic recording medium and thus sensitive to leakageflux from the magnetic recording medium is continuous in the directionof the track width. The provision of the notches 40 at the centralportions of the upper cores 13 and 14 on the side of the MR film 15permits the leakage flux to flow while branching right and left in thedirection of the track width, thus providing the same advantage as theseventh and eighth embodiments.

FIG. 12 is a plan view of a magnetic core of a magnetic head assemblyaccording to a tenth embodiment. In this embodiment, notch 40 is formedonly at the core 13 which is sensitive to the leakage flux from themagnetic recording medium. The tenth embodiment will also provide thesame advantage as the ninth embodiment.

FIG. 13 is a plan view of a magnetic core of a magnetic head assemblyaccording to an eleventh embodiment. The upper and lower cores 13 and 14are each divided into two pieces 43 and 44, 41 and 42 in the directionof the track width, and moreover the magnetic permeability of the pieces41 and 43 is made different from that of the pieces 42 and 44.

By making the right and left sides of the magnetic core different fromeach other in magnetic permeability, a difference is produced betweenvariations in the amount of flux flowing into the right and left sidesof the core. Moreover, the difference will vary between when the headmoves to the right from the track center and when the head moves to theright from the center. Thus, by detecting a difference signal as in thefirst to sixth embodiments, the direction and amount of the track offsetof the magnetic head assembly can be detected.

FIG. 14 is a perspective view of a magnetic core of a magnetic headassembly according to a twelfth embodiment. The magnetic core of thisembodiment is formed such that the lower core (i.e., leading edge side)divided into pieces 11a and 11b in the direction of the track width andthe upper core 13 (i.e., trailing edge side) is not divided in thedirection of the track width. According to the magnetic head assembly ofsuch a form, continuous recording can be made in the direction of thetrack width at the time of recording and the leakage flux from themagnetic recording medium can be divided right and left in the directionof the track width at the time of reproducing. In this case, it isdesired that the divided lower cores 11a and 11b be placed on theopposite side to the running direction of the magnetic recording mediumas shown.

The above-described embodiments (from FIG. 2 to FIG. 8) are applicableto shiled-type MR head and yoke-type MR head shown in FIG. 1A and FIG.1B.

The embodiments (from FIG. 9 to FIG. 14) are also applicable to yoketype MR head shown in FIG. 1B.

Hereinafter, descriptions will be made of embodiments in which first andsecond magnetic detecting elements are disposed separated in thedirection of the track width. FIGS. 15 to 24 illustrate theseembodiments.

FIG. 15 is a perspective view of a magnetic head assembly according to athirteenth embodiment. Each of first and second magnetic detectingelements 50a and 50b, which are disposed separated in the direction ofthe track width and parallel to each other, comprises an MR film 15, apair of current supply electrodes 16 and 17 disposed to contact bothedges of the MR film which are opposed to each other in the direction ofthe track length and a signal detect electrode 18 disposed between thecurrent supply electrodes to contact the MR film.

Between the first and second magnetic detecting elements 50a and 50b aredisposed magnetic cores 51 to 53 in the form of a ring. A gap 54 isformed between the magnetic cores 51 and 52 which is in contact with themagnetic recording medium. Gaps are also formed between the cores 51 and53 and between the cores 52 and the MR films 15 of the magneticdetecting elements 50a and 50b are disposed to sandwich these gapsbetween the cores 51 and 53 and between 52 and 53 from the direction ofthe track width.

With the magnetic head assembly constructed as above, when the lowersurfaces of the magnetic cores 51 and 52 are brought into contact withthe magnetic recording medium, leakage flux based on signals recorded ontracks of the recording medium flows into the MR films 15 of themagnetic detecting elements 50a and 50b via the magnetic cores 51 to 53.As a result, the electrical resistance of the MR films varies with theamount of flux. In this case, the leakage flux divides into the MR filmsof the magnetic detecting elements 50a and 50b and thus the amount offlux flowing into each of the MR films can be detected independently.This permits the track offset and azimuth offset to be detected withhigher accuracy.

When a constant flow of direct current is produced in the MR filmthrough the current supply electrodes 16 and 17 and a difference betweena voltage developed between the electrodes 16 and 17 and a voltagedeveloped between the electrodes 17 and 18 is obtained as a detectsignal, the polarity and magnitude of the detect signals obtained forthe magnetic detecting elements 50a and 50b vary according to adifference in variation in electrical resistance between the MR films ofthe magnetic detecting elements deepening on track offset and azimuthoffset. The use of these detect signals permits tacking control andazimuth alignment of the read/write head.

FIG. 16 is a perspective view of a magnetic head assembly according to afourteenth embodiment. The feature of this magnetic head assembly isthat each of the MR films 15 shown in FIG. 15 is divided into two parts15a and 15b in the direction of the track length and the tip of thesignal detect electrode 18 is divided into two branches. Both of theends of the MR film 15a are in contact with the current supply electrode16 and one of the two branches of the signal detect electrode 18, whileboth of the ends of the MR film 15b are in contact with the currentsupply electrode 17 and the other of the two branches of the signaldetect electrode 18. The present embodiment also provides the sameadvantage as the embodiment of FIG. 15.

FIG. 17 is a perspective view of a magnetic head assembly according to afifteenth embodiment. In this embodiment, the electrode 17 shown in FIG.15 is removed and the electrodes 16 and 18 are in contact with both theends of the MR film 15 in each of the magnetic detecting elements 50aand 50b. The magnetic core 53 shown in FIG. 15 is integral with themagnetic core 52. It is supposed in this case that the electrodes 16 and18 are used for both current supply and signal detection.

In this embodiment, a constant direct current flow is produced in the MRfilm 15 to detect a voltage between the electrodes 16 and 18 and adifference between voltages obtained from the magnetic detectingelements 50a and 50b is obtained as a detect signal, thus permitting thetrack offset and azimuth offset to be detected.

FIG. 18 is a perspective view of a magnetic head assembly according to asixteenth embodiment. In this embodiment, the length of the MR films ofthe magnetic detecting elements 50a and 50b in the direction of thetrack length is made shorter that in the embodiment shown in FIG. 17 andthe MR films are disposed to sandwich only the gap formed between themagnetic cores 51 and 52 and its neighborhood in the direction of thetrack width. This embodiment also provides the same advantage as theembodiment shown in FIG. 17.

FIG. 19 is a perspective view of a magnetic head assembly according to aseventeenth embodiment. In this embodiment, each of the magnetic cores51 to 53 shown in FIG. 15 is divided into two pieces in the direction ofthe track width and a non-magnetic film (or superconducting film) 55 isdisposed between the two pieces of each magnetic core. According to thisembodiment, each of the magnetic cores is magnetically divided into twoin the direction of the track width and hence the leakage flux dividesinto the MR films 15 of the magnetic detecting elements 50a and 50b,thus permitting the amount of flux flowing into each of the MR films tobe detected independently. For this reason, the track offset and azimuthoffset can be detected with higher accuracy.

FIG. 20 is a perspective view of a magnetic head assembly according toan eighteenth embodiment. Each of the magnetic cores 51 to 53 shown inFIG. 16 are magnetically divided into two pieces with non-magnetic film(or superconducting film) 55 interposed therebetween as in theembodiment of FIG. 19.

FIG. 21 is a perspective view of a magnetic head assembly according to anineteenth embodiment. Each of the magnetic cores 51 and 52 shown inFIG. 17 are magnetically divided into two pieces with non-magnetic film(or superconducting film) 55 interposed therebetween.

FIG. 22 is a perspective view of a magnetic head assembly according to atwentieth embodiment. Of the magnetic cores 51 to 53 in FIG. 15 themagnetic cores 51 and 52 which are nearer to the magnetic recordingmedium are each magnetically divided into two pieces with non-magneticfilm (or superconducting film) 55 interposed therebetween.

FIG. 23 is a perspective view of a magnetic head assembly according to atwenty-first embodiment. Of the magnetic cores 51 to 53 in FIG. 16 themagnetic cores 51 and 52 which are nearer to the magnetic recordingmedium are each magnetically divided into two pieces with non-magneticfilm (or superconducting film) 55 interposed therebetween as in theembodiment of FIG. 22.

FIG. 24 is a perspective view of a magnetic head assembly according to atwenty-second embodiment. Of the magnetic cores 51 and 52 in FIG. 17 themagnetic core 51 which is nearer to the magnetic recording medium ismagnetically divided into two pieces with non-magnetic film (orsuperconducting film) 55 interposed therebetween.

It will be apparent that the embodiments of FIGS. 20 to 24 can providethe same advantage as the seventeenth embodiment shown in FIG. 19because each of magnetic cores is magnetically divided into pieces inthe direction of the track width.

As described above, according to the present invention, an MR film isdisposed parallel to the direction of the track width, at least a pairof current supply electrodes are provided which is in contact with bothends of the MR film in the direction of the track width or theirneighborhoods and at least one signal detect electrode is provided whichis narrower in width than the current supply electrodes and in contactwith the MR film between the current supply electrodes. A flow ofconstant current is produced in the MR film by the current supplyelectrodes and a signal having a voltage difference or a currentdifference corresponding to track offset and azimuth offset is detectedby the signal detect electrode. Thus, the track offset and azimuthoffset can be detected with high sensitivity even when tracks of a diskare made narrow in width while the merits of magnetic heads using MRfilms are utilized. In this case, detection with a still highersensitivity will be made possible by magnetically dividing that part ofa magnetic core for conducting leakage flux from magnetic recordingmedium to a magnetic film which is nearer to the recording medium intopieces in the direction of the track width.

According to the present invention, first and second magnetic detectingelements are provided which are disposed apart from each other in thedirection of the track width and each of which comprises an MR filmdisposed substantially parallel to the direction of the track length andat least a pair of electrodes which is in contact with both of the endsof the MR film in the direction of the track width or theirneighborhoods. The first and second magnetic detecting elements areadapted to detect a signal having a voltage difference or a currentdifference corresponding to track offset and azimuth offset. Therefore,the dimension of the head along the track width can be made small and asufficient area of the part adapted to sense the leakage flux from themagnetic recording medium in the MR film can be secured. Accordingly, itis possible to detect the track offset and azimuth offset with a highsensitivity in the case of disks with narrow tracks. In this case,detection with a still higher sensitivity will be made possible byproviding a magnetic core for conducting leakage flux to the magneticfilms of the first and second magnetic detecting elements between thefirst and second detecting elements and magnetically dividing that partof the magnetic core which is nearer to the recording medium into piecesin the direction of the track width.

Hereinafter, an embodiment of a magnetic disk system of the presentinvention will be described using a magnetic head assembly shown inFIGS. 26A. 26B and 26C.

FIG. 26A is a front view of the magnetic head assembly, FIG. 26B is aplan view of the head assembly seen from its underside and FIG. 26C is aside view of the head assembly. In FIGS. 26B and 26C, a coil 2 and alead wire 10 shown in FIG. 16A are omitted.

The magnetic head assembly (hereinafter referred to as the head) 1 isconstructed from a coil 2, a yoke 3, a pole tip 4, electrodes 5, 6 and7, a magnetic film 8 having the magnetoresistance effect (hereinafterreferred to as the MR film) and a gap 9. A recording head 11 isconstructed from the coil 2, the yoke 3 and the gap 9. The coil 2 iswound around the yoke 3. Two reproducing heads 12A and 12B areconstructed from the yoke 3, the pole tip 4, the electrodes 5, 6 and 7and the MR film 8. The MR film 8 is embedded in the gap at the tip ofthe yoke 3. The electrodes 5, 6 and 7 are formed on the surface of theMR film 8 to contact it. A lead wire 10 is connected to each of theelectrodes. The lead wires 10 are adapted to conduct a current to theelectrodes and detect the potential on the electrodes.

As with conventional magnetic heads, the recording of data on a magneticdisk (hereinafter referred to as a disk) serving as a magnetic recordingmedium is made by magnetizing the disk with leakage flux from the gapwhich is generated by a current flow in the coil 2 having its severalturns wound around the yoke 3 serving as a flux path. Data is recordedin a width corresponding to the track width W (refer to FIG. 26B).

In a disk recording/reproducing apparatus for reproducing data recordedon the disk, as shown in FIG. 28, a constant current source 13 isconnected between the electrodes 5 and 7 and a constant current 1 iscaused to flow through the MR film 8 in a fixed direction. A potentialdifference detecting circuit 14 detects a potential difference betweenthe electrodes 5 and 6 and a potential difference between the electrodes6 and 7. In this case, the input resistance of the potential differencedetecting circuit 14 is selected to be sufficiently high so that thereis no current flow between the intermediate electrode 6 and thepotential difference detecting circuit.

The electrical resistance of the MR film 8 with the magnetoresistanceeffect varies according to variations in flux caused by data recorded onthe disk. Here, let the potentials on the electrodes 5, 6 and 7 be V1,V2 and V3, respectively. Further, suppose that the resistance of the MRfilm between electrodes 5 and 6 is R1 and the MR film resistance betweenelectrodes 6 and 7 is R2. Then, the supply current I and the potentialsV1, V2 and V3 will be related by

    R1=(V1-V2) / I

    R2=(V2-V3) / I                                             (1)

The supply current I is constant and variation in flux is proportionalto variation in the resistance of the MR film 8. Thus, the followingrelations will be obtained.

    φ1∝R1∝(V1-V2)

    φ2∝R2∝(V2-V3)                            (2)

By the reproducing head 12A, the variation of flux which varies, in thedirection of the gap, within the width WB is detected as a variation ofthe resistance of the MR film in the region A between electrodes 6 and7. The electric potential difference (v1-v2) is detected as the outputsignal VA by the potential difference detecting circuit 14.

By the reproducing head 12B, the variation of flux which varies, in thedirection of the gap, within the width WA is detected as a variation ofthe resistance of the MR film in the region B between electrodes 5 and6. The electric potential difference (V2-V3) is detected as the outputsignal VB by the potential difference detecting circuit 14. Then, thedata recorded as the output signal VB is reproduced within the width WB.

In the present embodiment, only one electrode 6 is disposed between theelectrodes 5 and 7 to construct the two reproducing heads 12A and 12B.The electrode 6 is disposed at the middle point between the electrodes 5and 7. Thus, WB=WA=W/2.

If a number N of electrodes were disposed between the electrodes 5 and7, a number (N+1) of reproducing heads each having a reproduce widthdetermined by the spacing between adjacent electrodes would be realized.Since the MR film is adapted to detect variations in flux, the amplitudeof reproduced signals is constant independently of wavelengths of datarecorded on the disk. Therefore, there is no need for an AGC (Auto GainControl) circuit for compensating for reproducing signal width on innerand outer tracks of the disk.

FIG. 29 is a block diagram of a head positioning control system of themagnetic disk unit which includes the head 1, the constant currentsource 13 and the potential difference detecting circuit 14 which weredescribed in connection with FIGS. 26A to 28. In this embodiment, arotary type actuator is used as actuator 22 for moving the head on adisk 21.

An optical position sensor 23 is provided for detecting the displacementof the head 1 from the outside of the disk. The optical position sensor23 is constructed from a reflection type scale 24 in which reflectingportions and non-reflecting portions are disposed alternately and atregularly spaced intervals and two sets of optical sensor units (one ofwhich is a combination of light emitting devices and light receivingdevices) 25. The reflection type scale 24 is built in the moving portionof the actuator 22 and the optical sensor units 25 are mounted on adrive base 27. A read/write circuit 26 includes a read circuit havingthe constant current source 13 and the potential difference detectingcircuit 14 described in connection with FIG. 28.

To produce a position signal indicating the position of the head 1relative to a data track on the disk 21 from the reproduced signals VAand VB output from the reproducing heads 12A and 12B of the headassembly 1, peak detectors 28 and 29 and a subtracter 30 are provided.The position signal is applied to a tracking servo circuit 31. An A/Dcircuit and a track pulse generator 33. An digital output of the A/Dconverter 32 and track pulses from the track pulse generator 33 areapplied to a controller 35, which produces a desired speed signal. Asthe controller 35, a microprocessor may be used.

On the other hand, the two-phase position signal output from the opticalposition sensor 23 is converted to a position signal of a prescribedsignal form by a position signal producing circuit 37 and then processedby a differentiator 38 and a smoother 39 to produce a speed signal. Adifference between the speed signal and the desired speed signal iscalculated by the subtracter 40 to produce a speed error signal. Forswitching between the tracking control and the seek control, switchingbetween the speed error signal and the position signal output from thetracking servo compensating circuit 31 is made by a switch 41. A signalselected by the switch 41 is applied to a voice coil motor (VCM) driver42 which drives a voice coil motor which is a drive unit for an actuator22.

The reproduced signals from the reproducing heads 12A and 12B are alsoapplied to an adder 43, so that they are added together. Thereby, dataon the disk is reproduced.

Next, the operation of the magnetic disk unit will be described.

First, a description will be made of a method of recording adisk-formatting signal consisting of data of a prescribed format on anunrecorded disk at the time of initial use of the disk with reference toFIGS. 30 and 31.

FIG. 30 is a block diagram of a head positioning control system forinitial disk formatting. When the actuator 22 carrying the head assembly1 moves on the disk 21 along its radial line, a two-phase positionsignal (X, Y) shown in FIG. 31 are obtained from the optical positionsensor 23. The position signals X and Y are applied to compensationcircuit 52 via the position signal switching circuit 51, therebyperforming feedback position control on the actuator 22 so that themagnitude of the position signals becomes zero. That is, the headassembly 1 is located in a position where the position signals X and Ybecome zero. The compensation circuit 52 compensates for the phase andgain of the feedback servo loop. A zero point of the position signals Xand Y of FIG. 31 corresponds to the center of a predetermined data track(the 4N-th data track in the case of the figure) on the disk 21. Thus,the feedback position control permits the positioning of the headassembly 1 at a predetermined track pitch. The formatting data isrecorded on the whole surface of the disk 21 while the head assembly 1are positioned on each of the data tracks in that way.

Next, a description will be made of the tracking control of the headassembly 1 when data is read from a recorded track with reference withFIGS. 32 and 33. FIG. 32 illustrates peak values PA and PB of thereproduced outputs VA and VB of the reproducing heads 12A and 12B of thehead assembly 1 which are detected by the peak detectors 28 and 29 andthe waveform of the position signal VA-VB output from the subtracter 30which is obtained when the head assembly 1 moves on the disk along itsradial line. Since the amplitude of the reproduced outputs VA and VB ofthe reproducing heads 12A and 12B do not depend on recorded wavelengths,their peak values take a maximum value a when the reproducing heads areall located within the width of a data track. The amplitude of thereproduced outputs will decrease gradually as the reproducing headsshift from the data track to a unrecorded guard band. When thereproducing heads are located to extend over two data tracks as shown inFIG. 32, the amplitude of the reproduced outputs will become indefinitebecause of data interference between the data tracks. Supposing that thedata track width is w and the guard band width is WG, the maximum valueof the indefinite zone will be given by

    a·(w/2-WG) / (W/2)                                (3)

Supposing that WG=0.2W, the maximum value of the peak values PA and PBof the reproduced outputs VA and VB in the indefinite zone will be 0.6a.

By calculating PA-PB from the peak values PA and PB shown in (a) and (b)of FIG. 32, such a position signal (PA-PB) as shown in (c) of FIG. 32.The position signal (PA-PB) is zero at the center of each of the datatracks. As shown in FIG. 29, therefore, the position signal (PA-PB)output from the subtracter 30 is applied to the actuator 22 via theswitch 41 and the VCM driver 42 after being subjected to the gain andphase compensation in the tracking servo compensation circuit 31. Byperforming feedback position control so that PA-PB=0 holds. the headassembly 1 can be placed on the center of a data track.

In order to obtain more correct position signals, each of the peakdetectors 28 and 29 in FIG. 29 may be replaced with a synchronousdetector. In this case, the reproduced signal from the reproducing head12A is subjected to synchronous detection using the reproduced signalfrom the reproducing head 12B as a reference signal to obtain a signalSA shown in (a) of FIG. 33. Similarly, the reproduced signal from thereproducing head 12B is subjected to synchronous detection using thereproduced signal from the reproducing head 12A as a reference signal toobtain a signal SB shown in (b) of FIG. 33. The difference (SA-SB) isobtained by the subtracter 30 to produce a position signal (SA-SB) shownin (c) of FIG. 33.

Note that, in the case where the synchronous detection is used, thereference signals for the synchronous detection cannot be obtained whenthe reproducing heads 12A and 12B extend over two data tracks. For thisreason, the position signal (SA-SB) cannot be obtained in the zonesenclosed by broken lines indicated in (a), (b) and (c) of FIG. 33.Therefore, it is practically desired that the position signal (PA-PB)based on the peak detection in the arrangement of FIG. 29 and theposition signal (SA-SB) based on the synchronous detection be used incombination. That is, at first coarse tracking control is performed bythe use of the position signal (PA-PB) and subsequently fine trackingcontrol is performed by the use of the position signal (SA-SB).

Next, the tracking control of the head assembly when data is rewrittenon a recorded data track on which data has already been recorded inaccordance with the above format will be described. With the headassembly 1 having such a construction as shown in FIGS. 26A to 26c, itis impossible for the reproducing heads 12A and 12B to reproduce signalswhile data is recorded. In the general disk format, data is recorded inblocks of sectors. On each sector ID information and data are recorded.Assuming that the ID information, etc., are also recorded in the presentembodiment as in the disk format, data on ID information, etc., will beread from the other area than data recording area within a track even atthe time of recording. Thus, a position signal (PA-PB) or (SA-SB) (i.e.,a position error signal) is obtained from the other area than the datarecording area within a track and the tracking control is performed onthe basis of this position signal. The position signal (PA-PB) or(SA-SB) obtained immediately before the initiation of recording of datais held until recording of data is initiated. During a recording period,the signal is regarded as a position error signal, so that the samefeedback position control as above is performed.

Next, the seek control of the head from a track to another track will bedescribed with reference to FIGS. 33 and 34. In the arrangement of thedisk unit shown in FIG. 29, detection of the position of the head 1 isperformed by the track counter 34 which counts the number of trackpulses each generated by the track pulse generator 33 every time thehead crosses a track. The track pulse counter 33 may comprises acomparator which converts the position signal (PA-PB) to pulses as shownin FIG. 34.

As the comparator used as the track pulse generator 33, it is desirableto use what is referred to as a hysteresis comparator in which itsthreshold varies between when the input signal level increases and whenthe input signal level decreases. FIG. 34 illustrates a waveform whensuch a hysteresis comparator is used. The waveform of the track pulsesshown in FIG. 34 is produced when the seek is performed from the insideto the outside of the disk 21. In this example, the threshold when thesignal level varies in the positive direction is set to Vth, while thethreshold when the signal level varies in the negative direction is setto zero. When the seek is performed from the inside to the outside, onthe other hand, the threshold when the position signal varies in thepositive direction is set to zero, while the threshold when the positionsignal varies in the negative direction, the threshold is set to anon-zero value. Therefore, the track pulse waveform in the case of seekfrom the outside to the inside of the disk is the inverse of thatobtained when the seek is performed from the inside to the outside.

As can be seen from the foregoing, when a hysteresis comparator is usedas the track pulse generator 33, even if the position signal levelvaries minutely in the neighborhood of the zero level because of noiseand vibration of the head, any false track pulse will not be produced aslong as the level variation is limited below the threshold Vth. As aresult, an advantage arises in that no miscount of the tracks occurs.

To detect the speed of the head 1 required for seek control, thetwo-phase position signal X, Y from the optical position sensor 23 isused. The position signals X and Y are applied to the position signalproducing circuit 37 where they are converted to such a position signalas shown in (b) of FIG. 35 according to their relationship in magnitude.The position signal is produced by extracting only linear portions ofthe two-phase position signal X, Y shown in (a) of FIG. 35. The positionsignal output from the position signal producing circuit 37 is subjectedto differentiating process in the differentiator 38 to produce a speedsignal. The points of discontinuity of the position signal from theposition signal producing circuit 37 exhibit impulse-like waveformsbecause of the differentiating process. To remove this phenomenon, asmoothing process is performed by the smoother 39.

For example, when a seek instruction is issued, the head 1 is moved at ahigh speed from the track on which the head is positioned at present toa desired track, whereby high-speed seek is performed. To set a travelspeed of the head for the high-speed seek, a speed curve providingdesired speeds for intermediate tracks has been stored in the controller35.

Next, when the head 1 starts the seek operation, the controller 35 readsa count of the track counter 34 to find the current track position andoutputs data on a desired speed corresponding to the current trackposition. The desired speed data is converted to an analog desired speedsignal by the D/A converter 36 and then applied to the subtracter 40where the difference (speed error signal) between the desired speedsignal and the actual speed signal from the smoother 39 is obtained. Byfeeding the speed error signal back to the actuator 22 via the switch 41and the VCM motor 42 as a control signal, the feedback speed controlloop is formed. The high-speed seek of a desired track at a high speedby the head is performed by the above procedure.

When the head comes sufficiently close to the desired track, the controlsystem is switched from the seek control to the tracking control.Specifically, the controller 35 takes in the position signal (PA-PB) viathe A/D converter 32 when the head passes through a track one trackbefore the desired track and then observes variations of the positionsignal to decide whether the head has entered the area in which trackingcontrol is possible. When it is confirmed that the area has beenreached, switching is made from the seek control system to the trackingcontrol system.

The present invention is not limited to the above embodiments. Forexample, to detect the position of the head, the position signalobtained from the reproduced signals from the reproducing heads 12A and12B and the position signal output from the optical position sensor maybe used in combination. It is difficult to directly detect the datatrack position on the basis of the position signal from the opticalposition sensor because of deformation of disk due to variations intemperature and humidity and aging. However, to detect the head positionbetween track pulses obtained from the disk 21, the position signal fromthe optical position sensor 23 can be used. For example, the headposition between tracks may be detected by counting zero cross points ofthe two phase position signal (X, Y) from the optical position sensor23. It will also be possible to calculate the position of the head fromanalog level of the position signals X and Y.

Although, in the present embodiment, reproduced outputs of thereproducing heads 12A and 12B are subjected to signal processing (peakdetection or synchronous detection) and then their difference isobtained to produce the position signal, the position signal may beobtained by detecting the difference between the reproduced outputs.Depending on conditions, the mere difference between the reproducedoutputs may be defined as the position signal.

In the present embodiment, MR heads using MR films are used as thereproducing heads 12A and 12B. Instead, other types of flux sensitiveheads, so-called active heads may be used which detect a signal magneticfield from a disk as high-frequency characteristics (high-frequencypermeability, etc.) of a magnetic material and take out a variation ofthe high-frequency characteristics as a variation of an electric signal.

According to the embodiments of the magnetic disk unit of the magneticdisk system of the present invention, there is no need for areas inwhich servo information for positioning of a head is to be formed, thusavoiding a decrease in storage capacity due to servo information andincreasing the formatting efficiency.

The position signal (position error signal) for direct tracking iscontinuously obtained from data tracks. Thus, there is no thermaloff-track due to expansion and contraction of a disk, the trackabilityis improved because a high servo band is obtained and the settlingcharacteristics and disturbance characteristics are improved. Thispermits accurate positioning of the head, high track density and largecapacity.

Moreover, there is no need for two types of formatting as in theservo-surface and data-surface combined system. This permits quickestablishment of the disk system.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A magnetic disk system comprising a magnetic headand a servo control circuit for positioning the magnetic head, in whichsaid magnetic head comprises:a magnetic film having two ends and amagnetic resistance effect and disposed parallel to a direction of awidth of a track of a magnetic recording medium; a pair of currentsupplying electrodes in contact with both ends of said magneticresistance film; and a signal detecting electrode in contact with saidmagnetic resistance film and disposed at such an position between saidpair of current supplying electrodes that a first reproduced outputbetween said signal detecting electrode and a first one of said pair ofcurrent supplying electrodes equals to a second reproduced outputbetween said signal detecting electrode and a second one of said pair ofcurrent supplying electrodes when said magnetic film is centered overthe track of the magnetic recording medium, and said servo controlcircuit comprises: means for calculating a difference between said firstreproduced output and said second reproduced output to produce aposition signal of the magnetic head relative to the track; and meansfor controlling a position of the magnetic head based on the positionsignal.
 2. A magnetic disk system according to claim 1, in which theposition xc of said signal detecting electrode of said magnetic headsatisfies: ##EQU2## where Rs(x) is a reproducing sensitivitydistribution of the magnetic film andxc is a relative position of saidsignal detecting electrode with regard to a physical center (x=0) of themagnetic film, xc having an absolute value greater than
 0. 3. A magneticdisk system according to claim 1, in which said signal detectingelectrode of said magnetic head has a width narrower than a width ofeach of said pair of current supplying electrodes.
 4. A magnetic disksystem according to claim 3, in which the width of said signal detectingelectrode of said magnetic head is less than 1/3 of a width of each ofsaid pair of current supplying electrodes.
 5. A magnetic disk systemaccording to claim 1, in which said magnetic head further comprises:aninsulating film which is interposed between a first portion of saidsignal detecting electrode and said magnetic film, and only a secondportion of said signal detecting electrode which is adjacent to saidrecording medium is in contact with said magnetic film.
 6. A magneticdisk system comprising a magnetic head and a servo control circuit forpositioning the magnetic head, in which said magnetic head comprises:amagnetic film having two ends and magnetic resistance effect anddisposed parallel to a direction of a width of a track of a magneticrecording medium; a pair of current supplying electrodes in contact withboth ends of said magnetic resistance film; and a signal detectingelectrode in contact with said magnetic resistance film disposed betweensaid pair of current supplying electrodes and said servo control circuitcomprises: means for obtaining a first reproduced output between saidsignal detecting electrode and a first one of said pair of currentsupplying electrodes; means for obtaining a second reproduced outputbetween said signal detecting electrode and a second one of said pair ofcurrent supplying electrodes; means for storing a ratio of the firstreproduced output to the second reproduced output when the magnetic headis on-track; means for calculating a difference between said firstreproduced output and said second reproduced output to produce aposition signal of the magnetic head; means for correcting the positionsignal based on the stored ratio to generate a corrected positionsignal; and means for controlling a position of the magnetic head basedon the corrected position signal.
 7. A magnetic disk system according toclaim 6, which further comprises:a magnetic recording medium having atrack having a width wider than a width of the magnetic head; and meansfor obtaining the ratio of the first reproduced output to the secondreproduced when the magnetic head is positioned at the given track.
 8. Amagnetic disk system according to claim 6, in which said signaldetecting electrode is positioned such that the first reproduced outputis equal to the second reproduced output.
 9. A magnetic disk systemaccording to claim 8, in which the position xc of said signal detectingelectrode of said magnetic head is represented as follows: ##EQU3##where Rs(x) is a reproducing sensitivity distribution of the magneticfilm andxc is a relative position of said signal detecting electrodewith regard to a physical center (x=0) of the magnetic film.
 10. Amagnetic disk system according to claim 6, in which said signaldetecting electrode of said magnetic head has a width narrower than awidth of each of said pair of current supplying electrodes.
 11. Amagnetic disk system according to claim 10, in which the width of saidsignal detecting electrode of said magnetic head is less than 1/3 of awidth of each of said pair of current supplying electrodes.
 12. Amagnetic disk system according to claim 6, in which said magnetic headfurther comprises:an insulating film which is interposed between saidsignal detecting electrode and said magnetic film, and wherein only thatpart of said signal detecting electrode which is adjacent to saidrecording medium is in contact with said magnetic film.
 13. A method forservo-controlling a magnetic head comprising a magnetic film having twoends and a magnetic resistance effect and disposed parallel to adirection of a width of a track of a magnetic recording medium, a pairof current supplying electrodes in contact with both ends of saidmagnetic resistance film, and a signal detecting electrode in contactwith said magnetic resistance film and disposed between said currentsupplying electrodes, the method comprising the steps of:(a) obtaining afirst reproduced output between said signal detecting electrode and oneof said current supplying electrodes and a second reproduced outputbetween said signal detecting electrode and the other of said currentsupplying electrodes when the magnetic head is on-track; (b) obtainingand storing a ratio of the first reproduced output to the secondreproduced output when the magnetic head is on-track; (c) obtaining afirst reproduced output between said signal detecting electrode and afirst one of said pair of current supplying electrodes and a secondreproduced output between said signal detecting electrode and a secondone of said current supplying electrodes during reproduction of themagnetic recording medium; (d) means for calculating a differencebetween said first reproduced output and said second reproduced outputto produce a position signal of the magnetic head; (e) means forcorrecting the position signal based on the stored ratio to generate acorrected position signal; and (f) means for controlling a position ofthe magnetic head based on the corrected position signal.
 14. A methodaccording to claim 13, in which said step (a) comprises a substep ofpositioning the magnetic head at a given track of the magnetic recordingmedium having a width wider than a width of the magnetic head.